The protocol in the long term evolution (LTE) system is release 8 (R8), and the information reflecting the channel state information (CSI) has three forms: channel quality indication (CQI), pre-coding matrix indicator (PMI), and rank indicator (RI).
CQI is an indicator for measuring the quality of the downlink channel. In the 36-213 protocol, CQI is represented using an integer value from 0 to 15, which respectively represents different CQI levels. Different CQIs correspond to respective modulation manners and coding rates (i.e. modulation coding scheme, MCS), which have 16 situations in total, and they can be represented using 4-bit information.
PMI means that only in the transmission mode of closed loop spatial multiplexing, the user equipment (UE) tells the eNode B (eNB) to use what kind of pre-coding matrix to pre-code the physical downlink shared channel (PDSCH) sent to the UE according to the measured channel quality. The feedback granularity of PMI can be that the whole bandwidth feeds back one PMI or that the PMI is fed back according to the subband.
RI is used to describe the number of spatially independent channels and corresponds to the rank of a channel response matrix. Under the modes of open loop spatial multiplexing and closed loop spatial multiplexing, the UE needs to feed back RI information, while it does not need to feed back RI information under other modes. The rank of the channel matrix corresponds to the number of layers of the downlink transmission, therefore, the UE feeding back the RI information to the eNode B is exactly feeding back the number of layers of the downlink transmission.
The transport layer is the concept of multi-antenna “layer” in LTE and LTE-A, represents the number of effective independent channels in the spatial multiplexing and corresponds to the antenna ports in release 10 one by one, wherein the antenna port in release 10 is a logic port and the total number of the transport layers is precisely RI. In addition, in IEEE802.16m, layer corresponds to the concept of “MIMO stream” and they have the same physical meaning.
In the LTE system, the feedback of CQI, PMI or RI can be periodic feedback and can also be non-periodic feedback. CQI and PMI can be sent simultaneously, or CQI, PMI and RI can be sent simultaneously. Wherein, as to periodic feedback, if the UE does not need to send data, then the CSI of periodic feedback is transmitted over the physical uplink control channel (PUCCH) in the format of 2 or 2a or 2b (PUCCH format2/2a/2b), and if the UE needs to send data, then the CSI is transmitted over the physical uplink shared channel (PUSCH); and as to non-periodic feedback, it is only transmitted over the PUSCH.
In related art, another method is to rotate the LTE codebook using relevant matrix information of the channel, i.e. mathematical transformation of the codebook of release R8:
  C  =            R              1        2              ×          C              R        ⁢                                  ⁢        8            
where C represents the codebook obtained after the rotation of CR8, R=HHH, H is a channel matrix with a dimension of Nr×Nt, Nr is the number of receiving antennae, and Nt is the number of transmitting antennae.
Since the channel matrix information includes the distribution information of the characteristic vector, the codeword in the codebook will also be quantized in an area with a relatively bigger distribution probability regarding the distribution probability of the characteristic vector after being rotated, thereby further improving the quantization precision.
The long term evolution advanced (LTE-A) as the evolution standard of LTE needs to support larger system bandwidth (up to 100 MHz), and the average frequency spectrum efficiency and the frequency spectrum efficiency of the margin users of the cell need to be increased, and the protocol thereof is release 10 (R10). For this end, many new technologies have been introduced into the LTE-A system: (1) downlink high-level multiple input multiple output (MIMO), the downlink of the LTE system at most supports 4-antenna transmission while the introduction of high-level MIMO enables the LTE-A system to at most support 8-antenna transmission in the downlink, then the number of dimensions of the channel state matrix is increased; (2) coordinated multiple point transmission (CoMP transmission), this technology is to use the coordinated transmission of the transmitting antennae of a plurality of cells, then the UE may need to feed back the channel state information of a plurality of cells.
A plurality of antennae are used at the transmission end (eNB), and the transmission rate can be improved in the manner of spatial multiplexing, i.e. different data are transmitted at different antenna locations on the same time frequency resource at the transmission end. A plurality of antennae can also be used at the receiving end (UE), and all the antenna resources can be allocated to the same user in the situation of single user, such transmission form is referred to as single user-MIMO (SU-MIMO); in addition, different antenna space resources can be allocated to different uses in the situation of multiple user, and such transmission form is referred to as multiple user-MIMO (MU-MIMO). In the single transmission mode, the eNB can dynamically select the downlink SU-MIMO transmission or MU-MIMO transmission according to the reported channel state information, which is referred to as SU/MU MIMO dynamic switching.
Hereinafter, the general processing procedure of the transmission mode of dynamic switching between the single user-MIMO and multiple user-MIMO will be described below:
firstly, the transmission end sends a pilot to the user equipment for the user equipment to test the downlink channel state, and the user equipment estimates the downlink channel according to the received pilot information and determines the format of the feedback channel state information and reports the channel state information, then the eNB dynamically selects the downlink SU-MIMO transmission or MU-MIMO transmission mode according to the reported channel state information and carries out communication according to the selected transmission mode.
As to the transmission mode of dynamic switching between the single user-MIMO and multiple user-MIMO, on one hand, backward compatibility needs to be maintained so as to support the priority principle of SU-MIMO and be compatible with the feedback forms of CQI/PMI/RI of R8 as much as possible, on the other hand, forward compatibility needs to be taken into account so as to consider the support of MU-MIMO and COMP and ensure that the new technology has acceptable performance. The precision of the existing channel information reporting method is rather low, which causes the eNode B to be unable to correctly select the downlink channel used when sending data to the UE, thereby leading to the result that the MU-MIMO system cannot reach rational performance.